A wide array of fluid-irrigated, ultrasonically-operated cutting devices have been developed for ophthalmological surgical techniques such as phacoemulsification--a method for removing a cataract through a surgical incision in the eye. Examples of such devices are set forth in the following patents:
______________________________________ Patent No. Inventor ______________________________________ 3,589,363 Banko et al. 4,515,583 Sorich 4,808,154 Freeman 4,816,017 Hood et al. 4,816,018 Parisi ______________________________________
U.S. Pat. No. 3,589,363 to Banko et al. and U.S. Pat. No. 4,515,583 to Sorich disclose ultrasonic surgical instruments that utilize rigid outer sleeves.
U.S. Pat. No. 4,808,154 to Freeman discloses a phacoemulsification/irrigation and aspiration sleeve apparatus.
U.S. Pat. No. 4,816,017 to Hood et al. discloses an ultrasonic decoupling sleeve.
U.S. Pat. No. 4,816,018 to Parisi discloses an ultrasonic probe tip.
Fluid-irrigated, ultrasonically-operated cutting devices typical of the prior art, however, suffer from a number of deficiencies. In particular, most infusion sleeves used during phacoemulsification are made of silicone or a silicone-type material. The use of this type of infusion sleeve can cause fluid leakage between the incision edge in the eye and the exterior surface of the infusion sleeve, resulting from a need to make the incision in the eye larger than the infusion sleeve. This need is due to the compressibility of silicone or like materials which cannot be safely used when inserted through an incision in the eye where there is a minimal amount of clearance between the incision and the exterior of the silicone infusion sleeve.
When there is a minimal clearance between the exterior of the silicone infusion sleeve and the incision of the eye, the incision tends to compress the nonrigid silicone infusion sleeve against the vibrating tip which results in relative rubbing movement between the silicone sleeve and the vibrating tip. This relative movement generates undesirable heat as the needle vibrates. The generation of this heat is extremely undesirable inasmuch as it can result in thermal burns and shrinkage of the ocular tissue surrounding the silicone infusion sleeve. The burning and shrinkage of ocular tissue is a serious problem with sight-threatening implications.
In an attempt to reduce the infusion fluid leakage and the deleterious effects that can be caused by undesirable friction generated therefrom, some infusion sleeves have been constructed from rigid, non-compressible materials. Generally these materials have consisted of Teflon or metallic-based compositions. These rigid, infusion sleeves have been relatively successful in solving the problems of constriction of the path for fluid flow between the distal end of the infusion sleeve and the vibrating tip as well as the heat generation and thermal burns associated with malleable infusion sleeves; however, other problems persist with these noncompressible infusion sleeves.
While rigid sleeves are capable of being inserted through smaller incisions, which has the advantage of reducing leakage, there is still significant leakage. The primary cause of the persistent leakage between the rigid infusion sleeve and the eye incision is that the cross section of the rigid sleeve does not match the contour of the eye incision. As a consequence, there are fairly substantial gaps between the rigid sleeve exterior surface and the eye incision. This is because the collagen fiber structure of the cornea resists deformity and thus does not readily assume the shape of the infusion sleeve.
Additionally, vibrating tips have traditionally been made of titanium. While such tips are suitable for the task of vibrating ultrasonically to remove tissue, modification of the tip composition in a way that reduces friction without compromising mechanical integrity would be highly desirable.
The experience of the applicant, who has performed literally thousands of cataract eye operations, has shown that it is impossible, from a practical standpoint, to fully eliminate the problem of leakage during cataract surgery by means of a smaller incision and forcing the rigid infusion sleeve through it. While this may decrease wound leakage, it does not eliminate the problem and it causes the instrument to be so tightly held by the deformed incision that there is great difficulty in advancing and withdrawing the instrument through the incision. As will be apparent to those skilled in the art, during cataract surgery the instrument must be advanced and withdrawn many times through the incision as the fractured portions of the cataract are removed from the various locations within the anterior and posterior chambers of the eye.
In an attempt to prevent heat transmission to ocular tissues, the previously-incorporated Mackool patents teach use of an inner, rigid sleeve, surrounded by an outer, malleable sleeve. While this technique is effective in reducing heat generation, there remains room for improvement. The present invention provides such an improvement. The techniques of the present invention, as described hereinbelow, can be employed by themselves or in combination with any of the methods and apparatus described in the previously-incorporated Mackool patents.
Accordingly, there exists a need for an improved apparatus for performing cataract surgery.